3GPP Long Term Evolution (LTE) is a standard for mobile phone network technology. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS), and is a technology for realizing high-speed packet-based communication that can reach high data rates on both downlink and uplink channels. As illustrated in FIG. 1, LTE transmissions are sent from base stations 102, such as Node Bs (NBs) and evolved Node Bs (eNBs or eNodeBs) in a telecommunications network 100, to communication devices 104 (a.k.a., user equipments (UEs) 104). The base stations 102 may include an uplink scheduler 202 (see FIG. 2).
The LTE standard is primarily based on Orthogonal Frequency Division Multiplexing (OFDM) in the downlink, which splits the signal into multiple parallel sub-carriers in frequency, and Single Carrier Frequency Domain Multiple Access (SC-FDMA) in the uplink.
Currently, LTE does not support dedicated data channels; rather, shared channel resources are used in both the downlink and uplink transmissions. These shared resources, Downlink Shared Channel (DL-SCH) and Uplink Shared Channel (UL-SCH), are each controlled by a scheduler that assigns different parts of the downlink and uplink shared channels to different scheduling entities (e.g., UEs) for reception and transmission, respectively. These schedulers are in full control of in which sub-frame a UE should receive on DL-SCH, or is allowed to transmit on UL-SCH. Scheduling decisions are sent to each UE as downlink assignments and uplink grants. Downlink assignment information and uplink grants may be transmitted as Downlink Control Information (DCI), for instance, using L1/L2 control signaling.
The resource allocation to UEs on both the downlink and uplink is performed adaptively, taking into account considerations such as instantaneous traffic patterns and radio propagation characteristics of the each UE. In order to properly assign resources in LTE, the base station must be aware of the status of pending data in each UEs buffer. Information regarding the UE's buffer is currently communicated according to a standardized communication protocol illustrated in FIG. 2.
As shown in FIG. 2, scheduling of a UE may be initiated by the UE sending a scheduling request (SR) to a base station 102. The SR can be sent on a dedicated SR channel (D-SR) or on the contention based Random Access Channel (RA-SR). When receiving the SR from the UE, the base station may respond with an uplink scheduling grant, including information indicating the specific time/frequency resources the UE can use for an uplink transmission. Link adaptation is performed at the base station and the selected transport format is signaled to the UE.
Once the UE receives an uplink scheduling grant, the UE may then send a buffer status report (BSR) and/or data buffered by the UE for uplink transmission to network 100, depending on the size of the grant. The purpose of the BSR is to inform the base station (and thus, the scheduler) about the details of the UE's buffer status. This information includes, for instance, what kind of data and how many bits of data are in the UE's buffer at the time of the report. Currently, as illustrated in FIG. 3, uplink data, which is associated with a logical channel, is mapped by the UE to one of a maximum of four Logical Channel Groups (LCGs). Thus, the BSR reports on how many bits are contained in the UE's buffer (i.e., buffer size) for each of the corresponding LCGs. LTE currently defines two types of BSRs, long and short. The long BSR reports the amount of data for all four LCGs, while the short BSR reports only the amount of data for a single LCG.
The decision by the UE to send an SR may be triggered by a number of factors. For instance, a UE may be configured to send an SR to network 100 whenever new data is ready to be transmitted and the new data is associated with a logical channel having a higher priority than all of the logical channels with which the data already buffered for transmission is associated. Additionally, the UE may be configured to send an SR to network 100 whenever a certain amount of time has elapsed since the last transmission of a BSR, or whenever the serving cell changes.
The amount of resources granted by the base station can be of variable size, i.e., the uplink transmission that follows from the UE may contain a varied number of bits. However, the granted number of bits should be sufficient for a buffer status report to be included in the uplink transmission from the UE. If there are sufficient bits for additional information, the UE may include data from its buffer.
For each UE that it serves, the scheduler of the base station maintains its own LCGs corresponding to the LCGs of the UE, with estimates of the associated amount of data for the UE in each LCG. For clarity purpose, the LCGs, and corresponding information, maintained by the base station and scheduler may be noted as LCGBS, a scheduler-side LCG, or a base station/scheduler LCG. Similarly, the LCGs, and corresponding information, maintained by the UE may be noted as LCGUE, a UE-side LCG, or a UE LCG.
A Quality of Service (QoS) class identifier (QCI) is used to classify different services in order to achieve a QoS concept. QoS is used to assist the scheduler in prioritizing resource allocations among users and services, based on various requirements for service quality. QCIs classify different services, and the priority assigned to a given QCI/service indicates how important it is with respect to other QCIs/services. The priority is used by the scheduler; for instance, the service with highest priority should be scheduled first, while services with lower priority are scheduler after (all else being equal).
In the scheduler, the priority may be used to determine a “scheduling weight.” Higher scheduling weight UEs will be scheduled prior to the ones with lower weight. A UE's scheduling weight may also be based on other parameters, such as channel quality; however the UE's priority typically influences greatly the UE's scheduling weight. In a system that is highly loaded with high priority UEs (UEs with high priority data to transmit on the uplink), those UEs with lower priority may not get scheduled for a significant amount of time due to their lower scheduling weight caused by their lower priority. The phenomenon is known as “starvation”.
The Layer 3 (L3) of the LTE radio access network (RAN) contains the RRC (RRC) functionality of the radio network. Examples of RRC functionality are RRC connection setup, bearer setup, and handover procedures and configuration of measurements. The L3 control signaling carries information between the RRC layer in RAN and the corresponding layer in the wireless terminals (e.g., UEs), and is carried over so-called Signaling Radio Bearers (SRB) on the Physical Uplink Shared Channel (PUSCH) and Physical Downlink Shared Channels (PDSCH). The user plane data is carried on ordinary Radio Bearers (RB), and is also mapped to the PUSCH and PDSCH.
The performance of L3 control signaling, in terms of delay, directly impacts the quality of service (QoS) of the user plane data transmission. Since the L3 signaling and the user plane data are carried on the same physical channels (the PUSCH and PDSCH), the Signaling Radio Bearers (SRBs) need to be prioritized relative to other radio bearers. The allocation of PDSCH and PUSCH, to different radio bearers and Signaling Radio Bearers (SRBs), is administrated by the scheduler.
Under current technologies, the scheduling of grant transmission triggered by SRs remains inefficient. Because a UE may trigger an SR due to either the arrival of new data when all buffers of the UE are empty, or the arrival of data that has higher priority than the highest priority of the existing data, the base station and scheduler have limited information regarding priority of the pending data upon receipt of an SR. An SR can essentially be triggered by data having any priority level. Therefore, the scheduler must guess as to the priority of the data that caused the UE to send the SR. If the SR is not properly prioritized, the UE may be starved or lower priority data may be scheduled ahead of higher priority data, leading to inefficiencies.
Moreover, when a UE is not scheduled, the UE may keep sending SRs periodically and may also stay in discontinues transmission (DRX) awake mode which will cost the UE battery. In certain scenarios, when the SR is triggered by RRC signaling, if the UE is not scheduled quickly enough, the UE might drop.
Accordingly there exists a need for more efficient prioritization scheme for scheduling requests. Moreover, there exists a need for a method and device that limits starvation of UEs.